Formic acid and acetic acid production from corn cob by catalytic oxidation using O2

Direct conversion of raw biomass to fine chemicals is of significant conceptual and practical interest. Up to now, the direct conversion of raw biomass to fine chemicals is still a big challenge. The oxidation of biomass to formic acid (FA) and acetic acid (AA) is a promising industrial process in the future. In this work, we reported that a binary catalyst system of Keggin-type heteropoly acid H5PV2Mo10O40 + H2SO4 was efficient to directly convert corn cob, a highly abundant renewable agricultural waste, to FA and AA using O2 as the oxidant in aqueous solutions. The effects of catalyst amount, H2SO4 concentration, reaction temperature, reaction time and initial O2 pressure on the conversions of corn cob were investigated. Under optimized reaction conditions, corn cob was transformed with a FA yield of 42.5% and an AA yield of 9.1% (based on carbon) after 30 min of reaction at 170 °C. In the oxidation, the pH of the aqueous solution plays a key role. The influences of pH on solid degradation, reaction pathway and oxidation of the components of corn cob were discussed. Hemicellulose is oxidized rapidly followed by partly oxidation of lignin, and cellulose is the most difficult converted part. Products FA and AA mainly come from polysaccharides (hemicellulose and cellulose) and pH has a major influence on cellulose. The recycling of the catalyst system is demonstrated and shows good reusability.